Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having an improved light efficiency, a polarizer used in the liquid crystal display device, and a method of manufacturing the polarizer.
Discussion of the Related Art
A liquid crystal display (LCD) device is advantageous in that it enables low power consumption owing to a low operation voltage and portability. Due to these advantages, the LCD device is widely used in various fields, for example, notebook computers, monitors, mobile terminal, televisions, spacecrafts, aircrafts, etc.
The LCD device includes a lower substrate, an upper substrate, and a liquid crystal layer between the lower and upper substrates. As an electric field is applied to the LCD device, liquid crystal molecules of the liquid crystal layer are aligned so that a light transmittance is controlled, and thus an image is displayed on the LCD device.
Hereinafter, a related art LCD device will be described with reference to FIG. 1.
FIG. 1 is a cross-sectional view illustrating the related art LCD device. As shown in FIG. 1, the related art LCD device includes a backlight unit 10 and a liquid crystal panel 20.
The backlight unit 10 supplies light to the liquid crystal panel 20. Since the LCD device is not a self-emissive device, the LCD device is provided with the backlight unit 10 as a light source for supplying light toward a lower portion of the LCD device.
The backlight unit 10 includes a light emitting device 12, a light guide plate 14, an optical sheet 16, and a reflective plate 18. The light emitting device 12 is a device for emitting light, and a light emitting diode (LED) has been used as the light emitting device 12.
The light guide plate 14 is arranged to face the light emitting device 12. The light guide plate 14 changes a moving path of light to allow the light emitted from the light emitting device 12 to move toward the liquid crystal panel 20.
The optical sheet 16 is formed above the light guide plate 14. The optical sheet 16 allows light emitted through an upper surface of the light guide plate 14 to uniformly enter the liquid crystal panel 20. This optical sheet 16 includes a combination of a diffusion sheet and a prism sheet.
The reflective plate 18 is formed below the light guide plate 14. The reflective plate 18 reflects light, which is emitted toward a lower portion of the light guide plate 14, toward an upper portion of the light guide plate 14, whereby light efficiency can be improved.
The liquid crystal panel 20 includes an upper substrate 21, a lower substrate 22, a sealant 23, a liquid crystal layer 24, an upper polarizer 25 and a lower polarizer 26. The sealant 23 is formed at a corner of the upper substrate 21 and the lower substrate 22 to bond the upper and lower substrates 21 and 22 to each other.
The liquid crystal layer 24 is formed in an area between the upper substrate 21 and the lower substrate 22, which are bonded to each other by the sealant 23. Although not shown, a pixel electrode and a common electrode are formed in at least one of the upper substrate 21 and the lower substrate 22, whereby an alignment direction of the liquid crystal layer 24 is changed by an electric field between the pixel electrode and the common electrode.
The upper polarizer 25 is formed on the upper substrate 21, and the lower polarizer 26 is formed below the lower substrate 22. The lower polarizer 26 polarizes light toward a predetermined light axis. Therefore, the light emitted from the backlight unit 10 is polarized toward the predetermined light axis while passing through the lower polarizer 26 towards the liquid crystal layer 24.
The upper polarizer 25 includes a light axis perpendicular to the lower polarizer 26. Therefore, the light polarized while passing through the lower polarizer 26 becomes a black state by failing to pass through the upper polarizer 25 if its phase is not delayed while passing though the liquid crystal layer 24, whereas the light becomes a white state by passing through the upper polarizer 25 if its phase is delayed while passing though the liquid crystal layer 24. The phase delay of the polarized light may be controlled through the alignment state of the liquid crystal layer 24.
In the related art LCD device described as above, the light emitted from the light emitting device 12 passes through all of the light guide plate 14, the optical sheet 16, the lower polarizer 26, the lower substrate 22, the liquid crystal layer 24, the upper substrate 21 and the upper polarizer 25. In this case, much light is lost while the light passes through these layers, whereby a problem occurs in that light efficiency is deteriorated.